Speed reducing mechanisms of the epicyclic type are well known mechanical transmission mechanisms, which typically include an orbiting internal pinion gear which is provided with teeth on its external periphery. The number of teeth on the pinion gear is typically one or a few less than the number of teeth on an outer ring gear, such that a large speed reduction can be obtained between the orbital input and an output appropriately coupled to the internal pinion gear.
Such epicyclic transmissions have been provided in single, double and multiple stages in order to obtain any desired speed transmission ratio. However, gear systems of the type just described suffer from a number of disabilities. Firstly, such gearing systems are not particularly efficient in terms of the amount of torque which can be transmitted, and secondly, the gears are expensive to produce, inasmuch as each toothed member must be precisely cut. Such devices can transmit only a limited amount of torque due to the fact that only some small fraction of the gear teeth are in contact at any given instant. It will be appreciated that it is impossible to design an internal pinion type speed reducing mechanism so that a large percentage of the torque transmitting elements (teeth) are in torque transmitting engagement at all times.